This is a phrase often used by lawyers (at least the ones onLaw and Order) to protest testimony
in open court that might be prejudicial to their side because once something is
said, even if an objection to it is sustained by the judge, the jury has heard
the words. You cannot take them back. You cannot unring the bell.

https://en.wikipedia.org/wiki/Unring_the_bell

The same is true this political season.

There is nothing that Donald Trump can say that can override
the despicable things he has said about Muslims, women, protestors, or
Mexicans. That bell cannot be unrung and his supporters wouldn’t want him to
anyway. Mr. Trump is speaking to the worst elements in the American
psyche—superiority over other peoples, the need to create jobs for those
without the needed skills, the idea that we can dominate world commerce by
ourselves, or that we can crush any opposition with our armed forces without
consequences to our people or our treasure. These are all lies. Furthermore,
like all good con men, Mr. Trump knows exactly what he is doing. He is a truly
awful person clanking at any bell in sight to focus attention on himself. He’s
more like a fire siren than a bell. If he’s a bell, he’s a cowbell. No, we don’t
need more cowbell.

There is no amount of hiding that Dr. DePinho can do to
remedy what his Moon Shot has begotten. The loss of clinical talent from MD
Anderson has been staggering and there is no way that some new assistant
professor can replace the clinical insight of an experienced professor who has
left, been fired, or simply retired. The same is true in MD Anderson’s
administration where what many thought was already an over proliferation of
vice presidents has grown like research buildings on the South Campus. Someone
is filling up the Good Ship Mendelsohn on the mid-campus and it is not with people
who generate revenue or new knowledge.

What the people who oversee the University of Texas in
Austin do not comprehend is that nothing they or Dr. DePinho or his FORDs can
do can unring the bell they cracked like the one in Philadelphia in 1776. This
bell of bad deeds cannot be unrung.

In our national politics, in our diplomatic relationships,
and in those relationships on which the MD Anderson depends for efficiency,
what you say and how you say it from a leadership pulpit matters. People
remember when you say you are going to build a wall and have the Mexicans pay
for it when you know or should know that this is a terrible idea. (Not to
mention net people movement has been towards Mexico and away from the US of
late). And walls won’t stop drugs from
coming in by air or by tunnel.

They
also remember statements about curing cancer and investing in one’s own
companies.

These many bells cannot be unrung.

And
therefore never send to know for whom the bell tolls; It tolls for thee.